Encryption method, decryption method, and related apparatus

ABSTRACT

Embodiments of the present application provide an encryption method, a decryption method, and a related apparatus. The encryption method includes: generating a keystream, where the keystream is used to encrypt a part of data to be encrypted in an initial layer-3 message, and the part of data to be encrypted includes small data; generating, by performing an exclusive OR operation on the keystream and the initial layer-3 message, an initial layer-3 message in which the part of data is encrypted; and sending the initial layer-3 message in which the part of data is encrypted, where the initial layer-3 message includes an added encryption indication, and the encryption indication is used to indicate that the part of data to be encrypted in the initial layer-3 message is encrypted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent Application No. PCT/CN2012/083661, filed on Oct. 29, 2012, which claims priority to Chinese Patent Application No. 201110331957.0, filed on Oct. 27, 2011, both of which are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present application relates to the field of wireless communications technologies, and in particular, to an encryption method, a decryption method, and related apparatuses.

BACKGROUND

Machine to machine (M2M) technology, a combination of wireless communication technologies and information technologies, is a technology that allows machines to directly communicate with each other without human intervention.

M2M communication is also called machine type communication (MTC). An M2M communication system is significantly different from a traditional human to human (H2H) communication system. The M2M communication system has many features of the machine type communication due to the large number of devices, low mobility, low communication traffic, and the like. The M2M communications system is referred to as an MTC communications system in the current Third Generation Partnership Project (3GPP) standard, and in the case of small data transmission (i.e. transmission small data), a short message service (SMS) or an Internet Protocol (IP) packet starts to be used to implement communications between the machines.

When SMS small data or IP packet small data is encapsulated in a tracking area update (TAU) request or a new initial layer-3 message, it needs to be considered how to provide confidentiality protection for the small data part of the initial layer-3 message and for other parameters that require protection.

SUMMARY

The present application provides an encryption method, a decryption method, and related apparatuses, so as to provide confidentiality protection for a part of data to be encrypted in an initial layer-3 message.

One aspect of the present application provides an encryption method, including:

-   -   generating a keystream, where the keystream is used to encrypt a         part of data to be encrypted in an initial layer-3 message, and         the part of data to be encrypted includes small data; and         generating, by performing an exclusive OR operation on the         keystream and the initial layer-3 message, an initial layer-3         message in which the part of data is encrypted; and     -   sending the initial layer-3 message in which the part of data is         encrypted, where the initial layer-3 message includes an added         encryption indication, and the encryption indication is used to         indicate that the part of data to be encrypted in the initial         layer-3 message is encrypted, so that a network side generates a         keystream according to the added encryption indication, and then         decrypts, according to the generated keystream, the initial         layer-3 message in which the part of data is encrypted.

Another aspect of the present application further provides a decryption method, including:

-   -   receiving an initial layer-3 message in which a part of data is         encrypted, where the initial layer-3 message includes an added         encryption indication, and the encryption indication is used to         indicate that the part of data to be encrypted in the initial         layer-3 message is encrypted;     -   generating a keystream according to the added encryption         indication in the initial layer-3 message, where the keystream         is used to decrypt the part of encrypted data in the initial         layer-3 message, and the part of encrypted data includes small         data; and     -   generating, by performing an exclusive OR operation on the         keystream and the initial layer-3 message, an initial layer-3         message in which the part of data is decrypted.

another aspect of the present application provides an encryption apparatus, including:

-   -   a generating unit, configured to generate a keystream, where the         keystream is used to encrypt a part of data to be encrypted in         an initial layer-3 message, and the part of data to be encrypted         includes small data;     -   a processing unit, configured to generate, by performing an         exclusive OR operation on the keystream that is generated by the         generating unit and the initial layer-3 message, an initial         layer-3 message in which the part of data is encrypted; and     -   a transmission unit, configured to send the initial layer-3         message in which the part of data is encrypted and that is         processed by the processing unit, where the initial layer-3         message includes an added encryption indication, and the         encryption indication is used to indicate that the part of data         to be encrypted in the initial layer-3 message is encrypted.

another aspect of the present application provides a decryption apparatus, including:

-   -   a transmission unit, configured to receive an initial layer-3         message in which a part of data is encrypted, where the initial         layer-3 message includes an added encryption indication, and the         encryption indication is used to indicate that the part of data         to be encrypted in the initial layer-3 message is encrypted;     -   a generating unit, configured to generate a keystream according         to the added encryption indication in the initial layer-3         message, where the keystream is used to decrypt the part of         encrypted data in the initial layer-3 message, and the part of         encrypted data includes small data; and     -   a processing unit, configured to generate, by performing an         exclusive OR operation on the keystream and the initial layer-3         message, an initial layer-3 message in which a part of data is         decrypted.

It can be learned from the foregoing technical solutions that the embodiments of the present application have the following advantages:

-   -   according to the embodiments of the present application, a         keystream is used to encrypt a part of data to be encrypted in         an initial layer-3 message, and the part of data to be encrypted         includes small data; an initial layer-3 message in which the         part of data is encrypted is generated by performing an         exclusive OR operation on the keystream and the initial layer-3         message; and the initial layer-3 message in which the part of         data is encrypted is sent, where the initial layer-3 message         includes an added encryption indication, and the encryption         indication is used to indicate that the part of data to be         encrypted in the initial layer-3 message is encrypted. In this         way, a part of data in the initial layer-3 message can be         encrypted, thereby avoiding a problem that confidentiality         protection cannot be performed on an initial layer-3 message in         the prior art, and ensuring secure transmission of small data.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of the present application more clearly, the following briefly introduces the accompanying drawings used in describing the embodiments. Apparently, the accompanying drawings in the following description show merely some embodiments of the present application, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

FIG. 1 is a flow diagram of an encryption method according to an embodiment of the present application;

FIG. 2 is a schematic diagram of an encryption method according to another embodiment of the present application;

FIG. 3 is a flow diagram of a decryption method to an embodiment of the present application;

FIG. 4 is a simplified block diagram of an encryption apparatus according to an embodiment of the present application;

FIG. 4a is a simplified block diagram of an encryption apparatus according to another embodiment of the present application;

FIG. 4b is a simplified block diagram of an encryption apparatus according to another embodiment of the present application;

FIG. 4c is a simplified block diagram of an encryption apparatus according to another embodiment of the present application;

FIG. 4d is a simplified block diagram of an encryption apparatus according to another embodiment of the present application;

FIG. 5 is a simplified block diagram of a decryption apparatus according to an embodiment of the present application;

FIG. 5a is a simplified block diagram of a decryption apparatus according to another embodiment of the present application;

FIG. 5b is a simplified block diagram of a decryption apparatus according to another embodiment of the present application;

FIG. 5c is a simplified block diagram of a decryption apparatus according to another embodiment of the present application; and

FIG. 5d is a simplified block diagram of a decryption apparatus according to another embodiment of the present application.

DETAILED DESCRIPTION

To make the objectives, technical solutions, and advantages of the embodiments of the present application more comprehensible, the following clearly describes the technical solutions in the embodiments of the present application with reference to the accompanying drawings. Apparently, the described embodiments are merely a part of the embodiments of the present application rather than all of the embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

The embodiments of the present application provide an encryption method, a decryption method, and related apparatuses, so as to provide confidentiality protection for a part of data to be encrypted in an initial layer-3 message.

In an SMS transmission scheme of the existing technology, for transmission of mobile originated (MO) SMS small data or IP packet small data, encrypted uplink SMS small data or IP packet small data is encapsulated in a tracking area update (TAU) request or a new initial layer-3 message; and encrypted downlink SMS small data or IP packet small data is encapsulated in a downlink non-access stratum (NAS) transport message of an S1 interface. For transmission of mobile terminated (MT) SMS small data or IP packet small data, encrypted downlink SMS small data or IP packet small data is encapsulated in a downlink NAS transport message of the S1 interface; and encrypted uplink SMS small data or IP packet small data is encapsulated in an uplink NAS transport message of the S1 interface.

In the above small-data transmission scheme, NAS messages carried in the downlink non-access stratum transport message and the uplink non-access stratum transport message of the S1 interface do not belong to initial layer-3 messages, and in a current encryption mechanism, confidentiality protection and integrity protection may be performed on these massages. However, for the TAU request or the new initial layer-3 message that is an initial layer-3 message, according to the current encryption mechanism, the integrity protection is performed when a valid security context is available, but the confidentiality protection is not performed on this type of message. However, according to a requirement of the small-data transmission scheme, confidentiality protection needs to be performed on SMS small data or IP packet small data. Therefore, when the SMS small data or IP packet small data is encapsulated in a TAU request or a new initial layer-3 message, how to provide confidentiality protection for a part of small data in the initial layer-3 message and for other parameters that require protection needs to be considered.

The present application provides the following technical solutions:

FIG. 1 is a schematic diagram of an encryption method according to an embodiment of the present application. The method includes the following steps:

-   -   101: Generate a keystream, where the keystream is used to         encrypt a part of data to be encrypted in an initial layer-3         message, and the part of data to be encrypted includes small         data.     -   102: Generate, by performing an exclusive OR operation on the         keystream and the initial layer-3 message, an initial layer-3         message in which the part of data is encrypted.     -   103: Send the initial layer-3 message in which the part of data         is encrypted, where the initial layer-3 message includes an         added encryption indication, and the encryption indication is         used to indicate that the part of data to be encrypted in the         initial layer-3 message is encrypted, so that a network side         generates a keystream according to the added encryption         indication, and then decrypts, according to the generated         keystream, the initial layer-3 message in which the part of data         is encrypted.

According to this embodiment of the present application, a keystream is used to encrypt a part of data to be encrypted in an initial layer-3 message, and the part of data to be encrypted includes small data; an initial layer-3 message in which the part of data is encrypted is generated by performing an exclusive OR operation on the keystream and the initial layer-3 message; and the initial layer-3 message in which the part of data is encrypted is sent, where the initial layer-3 message includes an added encryption indication, and the encryption indication is used to indicate that the part of data to be encrypted in the initial layer-3 message is encrypted. In this way, a part of data in the initial layer-3 message can be encrypted, thereby avoiding a problem that confidentiality protection cannot be performed on an initial layer-3 message in the prior art, and ensuring secure transmission of small data.

In this embodiment of the present application, an MTC communications system in the 3GPP standard implements machine-to-machine small-data communication by using NAS signaling to carry an SMS message or an IP packet, data that is transmitted during communication between machines is referred to as small data because the data amount is small, and the small data is usually carried in the SMS message or the IP packet. For transmission of MO SMS small data or IP packet small data, the SMS small data or IP packet small data is generally encapsulated in an initial layer-3 message. To implement encryption on a part of small data in an SMS message, the generated initial layer-3 message in this embodiment of the present application includes an added encryption indication, so that the network side is capable of identifying that the part of data in the initial layer-3 message is encrypted, and a receive end needs to decrypt the initial layer-3 message after receiving it. The initial layer-3 message may specifically include a TAU request message or a new initial layer-3 message. In a practical application, a specific application scenario determines which message in which SMS message small data or IP packet small data is carried, which is not limited herein. It should be noted that the new initial layer-3 message is an initial layer-3 message that is newly defined by the MTC communications system and is used to transmit small data.

In a practical application, the initial layer-3 message includes the added encryption indication, and one possible implementation manner may specifically include:

-   -   adding an integrity-protected and partly ciphered parameter to a         security header type parameter in the initial layer-3 message,         and setting the security header type parameter to the         integrity-protected and partly ciphered parameter.

It should be noted that a current security header type parameter may specifically include but is not limited to two parameters, where the two parameters are an integrity-protected parameter and an integrity-protected and ciphered parameter. In this embodiment of the present application, one integrity-protected and partly ciphered parameter is added to the Security header type and is used to indicate that a part of data to be encrypted in an initial layer-3 message is encrypted. After the integrity-protected and partly ciphered parameter is added, the security header type parameter is set to the integrity-protected and partly ciphered parameter, so that the network side identifies the part of encrypted data in the initial layer-3 message.

In a practical application, the initial layer-3 message includes the added encryption indication, and another possible implementation manner may specifically include: adding a small-data transmission indication to the initial layer-3 message, and setting the security header type parameter to an integrity-protected parameter.

In a practical application, the initial layer-3 message includes the added encryption indication, and another possible implementation manner may specifically include: adding a small-data transmission indication to the initial layer-3 message, and setting the security header type parameter to an integrity-protected and ciphered parameter.

It should be noted that in this embodiment of the present application, adding the small-data transmission indication to the initial layer-3 message indicates that the initial layer-3 message carries a part of encrypted SMS message small data or IP packet small data, and the network side needs to decrypt the part of encrypted data after receiving the initial layer-3 message.

In this embodiment of the present application, a keystream is generated to encrypt a part of data to be encrypted in an initial layer-3 message. The part of data to be encrypted in the initial layer-3 message in this embodiment of the present application includes but is not limited to small data. In a practical application, because the small data is encapsulated in an SMS message or an IP packet, and encryption means that the whole SMS message or IP packet is encrypted, the part of data to be encrypted generally includes an SMS message or an IP packet but further includes an SMS message header or an IP header; and in a practical application, content included in the part of data to be encrypted is determined by a specific implementation scenario, and no limitations are set herein.

In an embodiment of the present application, a keystream may specifically be generated by using an evolved packet system encryption algorithm (EEA). FIG. 2 is a flow diagram of an encryption method according to another embodiment of the present application. For example, FIG. 2 shows a data encryption mechanism: Firstly, a transmit end encrypts a plaintext by performing an exclusive OR operation on the plaintext and on a keystream that is generated by using the EEA; then, after receiving a ciphertext, a receive end generates the keystream by using the EEA and decrypts the ciphertext by performing an exclusive OR operation on the ciphertext and the generated keystream. In FIG. 2:

-   -   KEY is an encrypted key parameter and may be used to generate         different keystreams for different users;     -   BEARER is a radio bearer identifier parameter and may be used to         generate different keystreams for different bearers of a same         user, and for NAS signaling, BEARER is a constant value 0x00;     -   DIRECTION refers to a transmission direction parameter and may         be used to generate different keystreams in different         transmission directions of a same bearer of a same user. For an         uplink message, a value of DIRECTION is 0; and for a downlink         message, a value of DIRECTION is 1;     -   COUNT is a counter value parameter and may be used to generate         different keystreams for same messages in a same transmission         direction of a same bearer of a same user;     -   LENGTH is a length parameter and may be used to generate a         keystream that has a same length as that of a plaintext. The         value of LENGTH affects only a length of the keystream and does         not affect bits in the keystream;     -   KEY STREAM BLOCK is a generated keystream;     -   PLAIN TEXT BLOCK is a part of data to be encrypted (that is,         plaintext); and     -   CIPHER TEXT BLOCK is the generated ciphertext.

In a practical application, a possible implementation manner for generating a keystream may specifically include:

-   -   setting a value of a length parameter (that is, LENGTH) of a         keystream that needs to be generated to a value of a length of a         part of data to be encrypted in an initial layer-3 message,         where the length parameter is an input parameter for the evolved         packet system encryption algorithm; and generating the keystream         by using the evolved packet system encryption algorithm and         using the length parameter as the input parameter, where:     -   it should be noted that the value of LENGTH of the keystream is         set to the value of the length of the part of data to be         encrypted in the initial layer-3 message, and then the keystream         is generated according to the EPS encryption algorithm. For         example, if the value of the length of the part of data to be         encrypted in the initial layer-3 message is 3 bits, the value of         LENGTH in the generated keystream is 3 bits; and     -   generating, by performing an exclusive OR operation on the         keystream and the part of data to be encrypted in the initial         layer-3 message, an initial layer-3 message in which the part of         data is encrypted. For example, if the value of the length of         the part of data to be encrypted in the initial layer-3 message         is 3 bits, the value of the input parameter LENGTH is set to 3;         it is assumed that the generated keystream is 101, and the part         of data to be encrypted in the initial layer-3 message is 110,         the part of encrypted data that is finally generated after the         exclusive OR operation is performed on the keystream and on the         part of data to be encrypted in the initial layer-3 message is         011.

In a practical application, another possible implementation manner for generating a keystream may specifically include:

-   -   setting a value of a length parameter of a keystream that needs         to be generated to a value of a length of a variable in an         initial layer-3 message or to a value of a length of the initial         layer-3 message, where the length parameter is an input         parameter for the evolved packet system encryption algorithm;         generating the keystream by using the evolved packet system         encryption algorithm and using the length parameter as the input         parameter; and truncating the generated keystream according to a         length of a part of data to be encrypted, where a length of the         keystream after truncating is the same as the length of the part         of data to be encrypted in the initial layer-3 message.

An implementation manner for generating an initial layer-3 message in which a part of data is encrypted is as follows: generating, by performing an exclusive OR operation on the keystream and on the part of data to be encrypted in the initial layer-3 message, an initial layer-3 message in which the part of data is encrypted.

It should be noted that the value of the input parameter LENGTH of the keystream is set to the value of the length of the initial layer-3 message or to the value of the length of the variable in the initial layer-3 message (however, the length of the variable in the initial layer-3 message is greater than the length of the part of data to be encrypted, and the value of the length of the initial layer-3 message is also greater than the length of the part of data to be encrypted); then the keystream is generated according to the EPS encryption algorithm; because only the part of data to be encrypted in the initial layer-3 message needs to be encrypted, the keystream is truncated after the keystream is generated, where the length of the keystream after the truncating is the same as the length of the part of data to be encrypted in the initial layer-3 message. When the keystream is truncated, it may be truncated in a manner of starting from the most significant bit to the least significant bit or in a manner of starting from the least significant bit to the most significant bit, or according to another truncation rule. This may be determined according to a specific implementation scenario in a practical application, and no limitations are set herein. For example, if the value of the length of the initial layer-3 message or the value of the length of the variable in the initial layer-3 message is 9, the value of LENGTH is set to 9; it is assumed that the generated keystream is 111010100, and the length of the part of data to be encrypted in the initial layer-3 message is 5 bits, the generated keystream is truncated in a manner of starting from the most significant bit to the least significant bit, and the keystream after the truncating is 11101; and it is assumed that the part of data to be encrypted in the initial layer-3 message is 00110, the part of encrypted data that is finally generated after the exclusive OR operation is performed on the keystream after the truncating and on the part of data to be encrypted in the initial layer-3 message is 11011.

It should be noted that if the value of the length of the variable in the initial layer-3 message equals the length of the part of data to be encrypted. For details, refer to the description about “setting a value of a length parameter (that is, LENGTH) of a keystream that needs to be generated to a value of a length of a part of data to be encrypted in an initial layer-3 message”. No further details are provided herein.

In a practical application, another possible implementation manner for generating a keystream may specifically include:

-   -   setting a value of LENGTH of a keystream that needs to be         generated to a value of a length of an initial layer-3 message         (the value of the length of the initial layer-3 message is         greater than a length of a part of data to be encrypted);         generating the keystream by using the evolved packet system         encryption algorithm and using the length parameter as an input         parameter; acquiring, according to a format of the initial         layer-3 message and the length of the part of data to be         encrypted, a start bit and a stop bit of the part of data to be         encrypted in the initial layer-3 message; reserving bits that         correspond to bits from the start bit to the stop bit in the         keystream; and replacing other bits except the bits from the         start bit to the stop bit in the keystream with 0.

It should be noted that the value of LENGTH of the keystream is set to the value of the length of the initial layer-3 message; the keystream is generated according to the EPS encryption algorithm; because only the part of data to be encrypted in the initial layer-3 message is encrypted, the start bit and the stop bit of the part of data to be encrypted in the initial layer-3 message may be acquired after the keystream is generated; and then bits that correspond to the bits from the start bit to the stop bit in the keystream are reserved, and other bits except the bits from the start bit to the stop bit in the keystream are replaced with 0, equivalent to that only the part of data to be encrypted in the initial layer-3 message is encrypted. For example, if the value of the length of the initial layer-3 message is 17, the LENGTH parameter is set to 17; it is assumed that the generated keystream is 01011010100111001, the start bit of the part of data to be encrypted in the initial layer-3 message is the 4^(th) bit, and the stop bit of the part of data to be encrypted is the 8^(th) bit; for the keystream, bits from the 4^(th) bit to the 8^(th) bit in the generated keystream need to be reserved (that is, bits 11010 are reserved), other bits in the keystream are replaced with 0, and a keystream that finally undergoes the exclusive OR operation with the initial layer-3 message is 00011010000000000. It is assumed that the initial layer-3 message is 11111010000000111, the generated initial layer-3 message in which the part of data is encrypted is 11100000000000111.

In a practical application, another possible implementation manner for generating a keystream may specifically include: setting a value of a LENGTH of a keystream to be generated to a value of a length of a variable in the initial layer-3 message (but the length of a variable part is greater than a length of part of data to be encrypted); generating the keystream by using the length parameter as an input parameter and using the evolved packet system encryption algorithm; acquiring, according to a format of the initial layer-3 message and the length of the part of data to be encrypted, a start bit and a stop bit of the part of data to be encrypted in the initial layer-3 message; reserving bits that correspond to bits from the start bit to the stop bit in the keystream; and replacing other bits than the bits from the start bit to the stop bit in the keystream with 0. An implementation manner for generating an initial layer-3 message in which a part of data is encrypted is as follows: generating, by performing an exclusive OR operation on the keystream and the variable in the initial layer-3 message, the initial layer-3 message in which the part of data is encrypted.

It should be noted that the value of LENGTH of the keystream is set to the value of the variable in the initial layer-3 message; the keystream is generated according to the EPS encryption algorithm; because only the part of data to be encrypted in the initial layer-3 message is encrypted, the start bit and the stop bit of the part of data to be encrypted in the initial layer-3 message may be acquired after the keystream is generated; and then bits that correspond to the bits from the start bit to the stop bit in the keystream are reserved, and the other bits in the keystream except the bits from the start bit to the stop bit are replaced with 0, equivalent to that only the part of data to be encrypted in the initial layer-3 message is encrypted. For example, it is assumed that the generated keystream is 01011010100111001, the start bit of the part of data to be encrypted in the initial layer-3 message is the 4^(th) bit, and the stop bit of the part of data to be encrypted is the 8^(th) bit, for the keystream, bits from the 4^(th) bit to the 8^(th) bit need to be reserved in the generated keystream (that is, bits 11010 are reserved), other bits in the keystream are replaced with 0, and a keystream that finally undergoes the exclusive OR operation with the initial layer-3 message is 00011010000000000. It is assumed that the variable part in the initial layer-3 message is 11111010000000111, the encrypted variable part is 11100000000000111.

In this embodiment of the present application, after the keystream is generated in step 101, the initial layer-3 message in which the part of data is encrypted may be obtained by performing an exclusive OR operation on the keystream and the initial layer-3 message, or the variable in the initial layer-3 message, or the part of data to be encrypted in the initial layer-3 message. For example, as shown in FIG. 2, CIPHER TEXT BLOCK may be obtained by performing an exclusive OR operation on PLAIN TEXT BLOCK and KEY STREAM BLOCK at the transmit end. Similarly, PLAIN TEXT BLOCK may be decrypted by performing an exclusive OR operation on CIPHER TEXT BLOCK and KEY STREAM BLOCK after the receive end receives CIPHER TEXT BLOCK.

In this embodiment of the present application, an initial layer-3 message includes an added encryption indication, so that after receiving the initial layer-3 message, a network side learns that a part of data to be encrypted in the initial layer-3 message is encrypted, then generates a keystream used to encrypt the part of data to be encrypted in the initial layer-3 message, and finally obtains, by performing an exclusive OR operation, the initial layer-3 message in which the part of data is encrypted, thereby providing confidentiality protection for the part of data to be encrypted in the initial layer-3 message.

The foregoing embodiments describe the encryption method according to an embodiment of the present application. The following describes a decryption method according to an embodiment of the present application. FIG. 3 is a schematic diagram of a decryption method according to an embodiment of the present application. Refer to FIG. 3. The method includes the following steps:

-   -   301: Receive an initial layer-3 message in which a part of data         is encrypted, where the initial layer-3 message includes an         added encryption indication, and the encryption indication is         used to indicate that the part of data to be encrypted in the         initial layer-3 message is encrypted.     -   302: Generate a keystream according to the added encryption         indication in the initial layer-3 message, where the keystream         is used to decrypt the part of encrypted data in the initial         layer-3 message, and the part of encrypted data includes small         data.     -   303: Generate, by performing an exclusive OR operation on the         keystream and the initial layer-3 message, an initial layer-3         message in which the part of data is decrypted.

In this embodiment of the present application, an initial layer-3 message in which a part of data is encrypted is received, where the initial layer-3 message includes an added encryption indication, and the encryption indication is used to indicate that the part of data to be encrypted in the initial layer-3 message is encrypted; a keystream is generated according to the added encryption indication in the initial layer-3 message, where the keystream is used to decrypt the part of encrypted data in the initial layer-3 message, and the part of encrypted data includes small data; and a decrypted initial layer-3 message is generated by performing an exclusive OR operation on the keystream and the initial layer-3 message. In this way, a part of data in the initial layer-3 message can be decrypted, thereby avoiding a problem that confidentiality protection cannot be performed on an initial layer-3 message in the prior art, and ensuring secure transmission of small data.

In this embodiment of the present application, for a receive end of an MTC communications system, after receiving an initial layer-3 message in which a part of data is encrypted and that is sent by a transmit end of the MTC communications system, the receive end learns, according to the added encryption indication in the initial layer-3 message, that the part of data in the initial layer-3 message is already encrypted.

In a practical application, for learning, according to the added encryption indication in the initial layer-3 message, that the part of data in the initial layer-3 message is already encrypted, one possible implementation manner is as follows:

-   -   acquiring, according to an integrity-protected and partly         ciphered parameter in the initial layer-3 message, that the part         of data in the initial layer-3 message is already encrypted.

It should be noted that if a security header type parameter in the initial layer-3 message is set to the integrity-protected and partly ciphered parameter, it can be learned that the part of data in the initial layer-3 message is already encrypted.

In a practical application, for learning, according to the added encryption indication in the initial layer-3 message, that the part of data in the initial layer-3 message is already encrypted, another possible implementation manner is as follows:

-   -   learning, according to a small-data transmission indication and         an integrity-protected parameter in the initial layer-3 message,         that the part of data in the initial layer-3 message is already         encrypted;     -   or learning, according to a small-data transmission indication         and an integrity-protected and ciphered parameter in the initial         layer-3 message, that the part of data in the initial layer-3         message is already encrypted.

That is, if a small-data transmission indication exists in the initial layer-3 message, it may be learned that the part of data in the initial layer-3 message is already encrypted regardless of whether the security header type parameter in the initial layer-3 message is set to the integrity-protected parameter or the integrity-protected and ciphered parameter.

In this embodiment of the present application, after it is learned that the part of data in the initial layer-3 message is already encrypted, the keystream is generated to decrypt the part of encrypted data in the initial layer-3 message. In this embodiment of the present application, the part of encrypted data in the initial layer-3 message includes but is not limited to small data. In a practical application, the small data is encapsulated in an SMS message or an IP packet, but encryption is to encrypt the entire SMS message or IP packet, and an encrypted part generally includes the SMS message or the IP packet, but also includes an SMS message header or an IP packet header.

In a practical application, a possible implementation manner for generating a keystream may specifically include:

-   -   setting a value of a length parameter (that is, LENGTH) of a         keystream that needs to be generated to a value of a length of a         part of encrypted data in the initial layer-3 message, where the         length parameter is an input parameter for an evolved packet         system encryption algorithm; and generating the keystream by         using the evolved packet system encryption algorithm and using         the length parameter as the input parameter.

It should be noted that the value of LENGTH of the keystream is set to the value of the length of the part of encrypted data in the initial layer-3 message, and then the keystream is generated according to the EPS encryption algorithm. For example, if the value of the length of the encrypted part in the initial layer-3 message is 3 bits, the value of LENGTH in the generated keystream is 3 bits.

An implementation manner for generating the initial layer-3 message in which the part of data is decrypted may include: generating, by performing an exclusive OR operation on the keystream and on the part of encrypted data in the initial layer-3 message, the initial layer-3 message in which the part of data is decrypted. For example, if the value of the length of the part of encrypted data in the initial layer-3 message is 3 bits, the value of LENGTH is set to 3; it is assumed that the generated keystream is 101, and the part of encrypted data in the initial layer-3 message is 011, the decrypted data that is finally generated after the exclusive OR operation is performed on the keystream and on the part of encrypted data in the initial layer-3 message is 110.

In a practical application, another possible implementation manner for generating a keystream may specifically include: setting a value of a length parameter to a value of a length of a variable in the initial layer-3 message or to a value of a length of the initial layer-3 message, where the length parameter is an input parameter for an evolved packet system encryption algorithm; generating a keystream by using the evolved packet system encryption algorithm and using the length parameter as the input parameter; and truncating the generated keystream according to the length of the part of encrypted data, where the length of the keystream after the truncating is the same as the length of the encrypted part in the initial layer-3 message.

An implementation manner for generating the initial layer-3 message in which the part of data is decrypted may include: generating, by performing an exclusive OR operation on the keystream and on the part of encrypted data in the initial layer-3 message, the initial layer-3 message in which the part of data is decrypted.

It should be noted that a value of LENGTH of a keystream is set to a value of a length of the initial layer-3 message, or to a value of a length of a variable in the initial layer-3 message (however, a length of a variable part needs to be greater than a length of a part of data to be encrypted, and the value of the length of the initial layer-3 message is also greater than the length of the part of data to be encrypted); then the keystream is generated according to an EPS encryption algorithm; because only an encrypted part in the initial layer-3 message needs to be decrypted, after the keystream is generated, the keystream is truncated to have the same length as that of the part of encrypted data in the initial layer-3 message. When the keystream is truncated, it may be truncated in a manner of starting from the most significant bit to the least significant bit or in a manner of starting from the least significant bit to the most significant bit, or according to another truncation rule. This may be determined according to a specific implementation scenario in a practical application, and no limitations are set herein. For example, if the value of the length of the initial layer-3 message or the value of the length of the variable in the initial layer-3 message is 9, the value of LENGTH is set to 9; it is assumed that the generated keystream is 111010100, and the length of the part of encrypted data in the initial layer-3 message is 5 bits, the generated keystream is truncated in a manner of starting from the most significant bit to the least significant bit, and the keystream after the truncating is 11101; and it is assumed that the part of encrypted data in the initial layer-3 message is 11011, the decrypted data that is finally generated after the exclusive OR operation is performed on the keystream after the truncating and on the part of encrypted data in the initial layer-3 message is 00110.

In a practical application, another possible implementation manner for generating a keystream may specifically include:

-   -   setting a value of a length parameter to a value of a length of         the initial layer-3 message (the value of the length of the         initial layer-3 message is greater than a length of a part of         encrypted data); generating a keystream by using the length         parameter as an input parameter and using the evolved packet         system encryption algorithm; acquiring, according to a format of         the initial layer-3 message and the length of the part of         encrypted data, a start bit and a stop bit of the part of         encrypted data that are in the initial layer-3 message;         reserving bits that correspond to bits from the start bit to the         stop bit in the keystream; and replacing other bits except the         bits from the start bit to the stop bit in the keystream with 0.

It should be noted that the value of LENGTH of the keystream is set to the value of the length of the initial layer-3 message; the keystream is generated according to the EPS encryption algorithm; because only the part of encrypted data in the initial layer-3 message is decrypted, the start bit and the stop bit of the part of encrypted data in the initial layer-3 message may be acquired after the keystream is generated; and then bits that correspond to the bits from the start bit to the stop bit in the keystream are reserved, and other bits in the keystream are replaced with 0, equivalent to that only the part of encrypted data in the initial layer-3 message is decrypted. For example, if the value of the length of the initial layer-3 message is 17, the LENGTH parameter is set to 17, and it is assumed that the generated keystream is 01011010100111001, the start bit of the part of encrypted data in the initial layer-3 message is the 4^(th) bit, and the stop bit of the part of encrypted data is the 8^(th) bit, for the keystream, bits from the 4^(th) bit to the 8^(th) bit need to be reserved in the generated keystream (that is, bits 11010 are reserved), other bits in the keystream are replaced with 0, and a keystream that finally undergoes the exclusive OR operation with the initial layer-3 message in which the part of data is encrypted is 00011010000000000. It is assumed that the initial layer-3 message in which the part of data is encrypted is 11100000000000111, and the decrypted initial layer-3 message is 11111010000000111. In a practical application, another possible implementation manner for generating a keystream may specifically include:

-   -   setting a value of a length parameter to a value of a length of         a variable of the initial layer-3 message (the value of the         length of the variable in the initial layer-3 message is greater         than a length of a part of encrypted data), where the length         parameter is an input parameter for an evolved packet system         encrypted algorithm; generating a keystream by using the evolved         packet system encryption algorithm and using the length         parameter as the input parameter; acquiring, according to a         format of the initial layer-3 message and the length of the part         of encrypted data, a start bit and a stop bit of the part of         encrypted data that are in the initial layer-3 message;         reserving bits that correspond to bits from the start bit to the         stop bit in the keystream; and replacing other bits except the         bits from the start bit to the stop bit in the keystream with 0.

An implementation manner for generating an initial layer-3 message in which a part of data is decrypted is as follows: generating, by performing an exclusive OR operation on the keystream and the variable in the initial layer-3 message, the initial layer-3 message in which the part of data is decrypted.

It should be noted that the value of LENGTH of the keystream is set to the value of the length of the variable in the initial layer-3 message; the keystream is generated according to the EPS encryption algorithm; because only the part of encrypted data in the initial layer-3 message is decrypted, the start bit and the stop bit of the part of encrypted data in the initial layer-3 message may be acquired after the keystream is generated; and then bits that correspond to bits from the start bit to the stop bit in the keystream are reserved, and other bits in the keystream are replaced with 0, equivalent to that only the part of encrypted data in the initial layer-3 message is decrypted. For example, if the value of the length of the variable in the initial layer-3 message is 17, the LENGTH parameter is set to 17, and it is assumed that the generated keystream is 01011010100111001, the start bit of the part of encrypted data in the initial layer-3 message is the 4^(th) bit, and the stop bit of the part of encrypted data is the 8^(th) bit, for the keystream, bits from the 4^(th) bit to the 8^(th) bit need to be reserved in the generated keystream (that is, bits 11010 are reserved), other bits in the keystream are replaced with 0, and a keystream that finally undergoes the exclusive OR operation with the initial layer-3 message in which the part of data is encrypted is 00011010000000000. It is assumed that the variable in the initial layer-3 message is 11100000000000111, a decrypted variable is 11111010000000111. In this embodiment of the present application, the decrypted initial layer-3 message may be obtained by performing the exclusive operation on the keystream and the initial layer-3 message, or a variable part of the initial layer-3 message, or an encrypted part of the initial layer-3 message. For example, as shown in FIG. 2, PLAIN TEXT BLOCK may be obtained by performing an exclusive OR operation on CIPHER TEXT BLOCK and KEY STREAM BLOCK at the receive end.

In this embodiment of the present application, it is learned, according to an added encryption indication in an initial layer-3 message, that a part of data in the initial layer-3 message is already encrypted; therefore, the part of encrypted data in the initial layer-3 message needs to be decrypted; then a keystream that is used to decrypt the part of encrypted data in the initial layer-3 message is generated; and finally a decrypted initial layer-3 message is obtained by performing an exclusive OR operation, thereby providing confidentiality protection for the encrypted part in the initial layer-3 message.

The foregoing embodiments describe the encryption method and the decryption method that are provided in the embodiments of the present application. The following describes an encryption apparatus and a decryption apparatus that are provided in the embodiments of the present application. The encryption apparatus and the decryption apparatus that are provided in the embodiments of the present application may be specifically applied to an MTC communications system. The MTC communications system has various applications, including but not limited to the following five major applications: automatic metering (for example, a water meter, an electricity meter, or a gas meter), remote monitoring, industry security and home automation, payment system (an automatic teller machine, a support terminal, a parking meter, and the like), and remote vehicle control (such as fleet management, toll collection, vehicle recovery, and insurance premium payment based on driving conditions). Vehicle-mounted applications include handsfree, remote communications system, embedded navigation, emergency call, remote diagnosis, embedded alarming, and the like.

An embodiment of the present application provides an encryption apparatus. FIG. 4 is a schematic diagram of an encryption apparatus according to an embodiment of the present application. As shown in FIG. 4, the encryption apparatus 400 includes:

-   -   a generating unit 401, configured to generate a keystream, where         the keystream is used to encrypt a part of data to be encrypted         in an initial layer-3 message, and the part of data to be         encrypted includes small data;     -   a processing unit 402, configured to generate, by performing an         exclusive OR operation on the keystream and the initial layer-3         message, an initial layer-3 message in which the part of data is         encrypted; and     -   a transmission unit 403, configured to send the initial layer-3         message in which the part of data is encrypted and that is         processed by the processing unit 402, where the initial layer-3         message includes an added encryption indication, and the         encryption indication is used to indicate that the part of data         to be encrypted in the initial layer-3 message is encrypted.

FIG. 4a is an apparatus embodiment of the present application. This embodiment is a further detailed embodiment of the embodiment shown in FIG. 4. The apparatus 400 further includes:

-   -   a first setting unit 404, configured to set a value of a length         parameter to a value of a length of the part of data to be         encrypted in the initial layer-3 message, where the length         parameter is an input parameter for an evolved packet system         encryption algorithm.

The generating unit 401 is specifically configured to generate a keystream by using the evolved packet system encryption algorithm and using the length parameter as the input parameter, where the length parameter is set by the first setting unit 404.

The processing unit 402 is specifically configured to generate, by performing an exclusive OR operation on the keystream that is generated by the generating unit 401 and the part of data to be encrypted in the initial layer-3 message, the initial layer-3 message in which the part of data is encrypted.

FIG. 4b is a schematic diagram of an encryption apparatus according to another embodiment of the present application. The encryption apparatus 400 further includes:

-   -   a second setting unit 405, configured to set a value of a length         parameter to a value of a length of a variable in the initial         layer-3 message, where the length parameter is an input         parameter for the evolved packet system encryption algorithm.

The generating unit 401 is specifically configured to generate a keystream by using the evolved packet system encryption algorithm and using the length parameter as the input parameter, where the length parameter is set by the second setting unit 405.

The encryption apparatus 400 further includes:

-   -   a first format processing unit 406, configured to acquire,         according to a format of the initial layer-3 message and a         length of the part of data to be encrypted, a start bit and a         stop bit of the data to be encrypted in the initial layer-3         message; reserve bits that correspond to bits from the start bit         to the stop bit in the keystream; and replace other bits except         the bits from the stop bit to the stop bit in the keystream with         0.

The processing unit 402 is specifically configured to generate, by performing an exclusive OR operation on the keystream that is processed by the first format processing unit 406 and the variable in the initial layer-3 message, the initial layer-3 message in which the part of data is encrypted.

FIG. 4c is a schematic diagram of an encryption apparatus according to another embodiment of the present application. The encryption apparatus 400 further includes:

-   -   a third setting unit 407, configured to set a value of a length         parameter to a value of a length of the initial layer-3 message,         where the length parameter is an input parameter for the evolved         packet system encryption algorithm.

The generating unit 401 is specifically configured to generate a keystream by using the evolved packet system encryption algorithm and using the length parameter as the input parameter, where the length parameter is set by the third setting unit 407.

The encryption apparatus 400 further includes:

-   -   a second format processing unit 408, configured to acquire,         according to a format of the initial layer-3 message and a         length of the part of data to be encrypted, a start bit and a         stop bit of the data to be encrypted in the initial layer-3         message; reserve bits that correspond to bits from the start bit         to the stop bit in the keystream; and replace other bits except         the bits from the stop bit to the stop bit in the keystream with         0.

FIG. 4d is a schematic diagram of an encryption apparatus according to another embodiment of the present application. The encryption apparatus 400 further includes:

-   -   a fourth setting unit 409, configured to set a value of a length         parameter to a value of a length of a variable in the initial         layer-3 message or a value of a length of the initial layer-3         message, where the length parameter is an input parameter for         the evolved packet system encryption algorithm.

The generating unit 401 is specifically configured to generate a keystream by using the evolved packet system encryption algorithm and using the length parameter as the input parameter, where the length parameter is set by the fourth setting unit 409.

The encryption apparatus 400 further includes:

-   -   a third format processing unit 410, configured to truncate the         generated keystream according to a length of the part of data to         be encrypted, where a length of the truncated keystream is the         same as a value of the length of the part of data to be         encrypted in the initial layer-3 message.

The processing unit 402 is specifically configured to generate, by performing an exclusive OR operation on the keystream that is processed by the third format processing unit 410. and the part of data to be encrypted in the initial layer-3 message, the initial layer-3 message in which the part of data is encrypted

It should be noted that the initial layer-3 message is a tracking area update request message TAU request or a new initial layer-3 message.

According to the apparatus in the present application, a keystream is generated, where the keystream is used to encrypt a part of data to be encrypted in an initial layer-3 message, and the part of data to be encrypted includes small data; an initial layer-3 message in which the part of data is encrypted is generated by performing an exclusive OR operation on the keystream and the initial layer-3 message; and the initial layer-3 message in which the part of data is encrypted is sent, where the initial layer-3 message includes an added encryption indication, and the encryption indication is used to indicate that the part of data to be encrypted in the initial layer-3 message is encrypted. In this way, a part of data in the initial layer-3 message can be encrypted, thereby avoiding a problem that confidentiality protection cannot be performed on an initial layer-3 message in the prior art, and ensuring secure transmission of small data.

FIG. 5 is a schematic diagram of a decryption apparatus according to an embodiment of the present application. The decryption apparatus 500 includes:

-   -   a transmission unit 501, configured to receive an initial         layer-3 message in which a part of data is encrypted, where the         initial layer-3 message includes an added encryption indication,         and the encryption indication is used to indicate that the part         of data to be encrypted in the initial layer-3 message is         encrypted;     -   a generating unit 502, configured to generate a keystream         according to the added encryption indication in the initial         layer-3 message, where the keystream is used to decrypt the part         of encrypted data in the initial layer-3 message, and the part         of encrypted data includes small data; and     -   a processing unit 503, configured to generate, by performing an         exclusive OR operation on the keystream and the initial layer-3         message, an initial layer-3 message in which the part of data is         decrypted.

FIG. 5a is a schematic diagram of a decryption apparatus according to another embodiment of the present application. The embodiment shown in FIG. 5a is a further detailed embodiment of the embodiment shown in FIG. 5. The decryption apparatus 500 includes:

-   -   a first setting unit 504, configured to set a value of a length         parameter to a value of a length of the part of encrypted data         in the initial layer-3 message, where the length parameter is an         input parameter for an evolved packet system encryption         algorithm.

The generating unit 502 is specifically configured to generate a keystream by using the evolved packet system encryption algorithm and using the length parameter as the input parameter, where the length parameter is set by the first setting unit 504.

The processing unit 503 is specifically configured to generate, by performing an exclusive OR operation on the keystream that is generated by the generating unit 502. and the part of encrypted data in the initial layer-3 message, the initial layer-3 message in which the part of data is decrypted

FIG. 5b is a schematic diagram of a decryption apparatus according to another embodiment of the present application. The embodiment shown in FIG. 5b is a further detailed embodiment of the embodiment shown in FIG. 5. The decryption apparatus 500 further includes:

-   -   a second setting unit 505, configured to set a value of a length         parameter to a value of a length of a variable in the initial         layer-3 message, where the length parameter is an input         parameter for the evolved packet system encryption algorithm.

The generating unit 502 is specifically configured to generate a keystream by using the evolved packet system encryption algorithm and using the length parameter being used as the input parameter, where the length parameter is set by the second setting unit 505.

The decryption apparatus 500 further includes:

-   -   a first format processing unit 506, configured to acquire,         according to a format of the initial layer-3 message and a         length of the part of encrypted data, a start bit and a stop bit         of the encrypted data in the initial layer-3 message; reserve         bits that correspond to bits from the start bit to the stop bit         in the keystream; and replace other bits except the bits from         the stop bit to the stop bit in the keystream with 0.

The processing unit 503 is specifically configured to generate, by performing an exclusive OR operation on the keystream that is processed by the first format processing unit 506 and the variable in the initial layer-3 message, the initial layer-3 message in which the part of data is decrypted.

FIG. 5c is a schematic diagram of a decryption apparatus according to another embodiment of the present application. The embodiment shown in FIG. 5c is a further detailed embodiment the embodiment shown in FIG. 5. The decryption apparatus 500 further includes:

-   -   a third setting unit 507, configured to set a value of a length         parameter to a value of a length of the initial layer-3 message,         where the length parameter is an input parameter for the evolved         packet system encryption algorithm.

The generating unit 502 is specifically configured to generate a keystream by using the evolved packet system encryption algorithm and using the length parameter being used as the input parameter, where the length parameter is set by the third setting unit 507.

The decryption apparatus 500 further includes:

-   -   a second format processing unit 508, configured to acquire,         according to a format of the initial layer-3 message and a         length of the part of encrypted data, a start bit and a stop bit         of the encrypted data in the initial layer-3 message; reserve         bits that correspond to bits from the start bit to the stop bit         in the keystream; and replace other bits except the bits from         the stop bit to the stop bit in the keystream with 0.

FIG. 5d is a schematic diagram of a decryption apparatus according to another embodiment of the present application. The embodiment shown in FIG. 5d is a further detailed embodiment of the embodiment shown in FIG. 5. The decryption apparatus 500 further includes:

-   -   a fourth setting unit 509, configured to set a value of a length         parameter to a value of a length of a variable in the initial         layer-3 message or a value of a length of the initial layer-3         message, where the length parameter is an input parameter for         the evolved packet system encryption algorithm.

The generating unit 502 is specifically configured to generate a keystream by using the evolved packet system encryption algorithm and using the length parameter being used as the input parameter, where the length parameter is set by the fourth setting unit 509.

The decryption apparatus 500 further includes:

-   -   a third format processing unit 510, configured to truncate the         generated keystream according to a length of the part of         encrypted data, where a length of the truncated keystream is the         same as a value of the length of the encrypted part in the         initial layer-3 message.

The processing unit 503 is specifically configured to generate, by performing an exclusive OR operation on the keystream that is processed by the third format processing unit 510 and the part of encrypted data in the initial layer-3 message, the initial layer-3 message in which the part of data is decrypted.

According to the apparatus provided in the present application, an initial layer-3 message in which a part of data is encrypted is received, where the initial layer-3 message includes an added encryption indication, and the encryption indication is used to indicate that a part of data to be encrypted in the initial layer-3 message is encrypted; a keystream is generated according to the added encryption indication in the initial layer-3 message, where the keystream is used to decrypt the part of encrypted data in the initial layer-3 message, and the part of encrypted data includes small data; and a decrypted initial layer-3 message is generated by performing an exclusive OR operation on the keystream and the initial layer-3 message. In this way, a part of data in the initial layer-3 message can be decrypted, thereby avoiding a problem that confidentiality protection cannot be performed on an initial layer-3 message in the prior art, and ensuring secure transmission of small data.

It should be noted that content about processes of information exchange, execution, and the like between various modules or units of the apparatuses is based on same thoughts as the method embodiments of the present application, and a technical effect brought by the apparatuses is the same as that of the method embodiments of the present application; and for specific content, reference may be made to the description in the method embodiment, as shown in FIG. 3, of the present application, and no further details are provided herein.

In this embodiment of the present application, it is learned, according to an added encryption indication in an initial layer-3 message, that a part of data in the initial layer-3 message is already encrypted; therefore, the part of encrypted data in the initial layer-3 message needs to be decrypted; then a keystream that is used to decrypt the part of encrypted data in the initial layer-3 message is generated; and finally a decrypted initial layer-3 message is obtained by performing an exclusive OR operation, thereby providing confidentiality protection for the part of data to be encrypted in the initial layer-3 message.

A person of ordinary skill in the art may understand that all or a part of the steps of the methods in the foregoing embodiments may be implemented by a program instructing relevant hardware. The program may be stored in a computer readable storage medium. The storage medium may be a read-only memory, a magnetic disk, or an optical disc.

The foregoing describes in detail an encryption method, a decryption method, and a related apparatus that are provided in the preset application. A person of ordinary skill in the art may make modifications to the specific implementations and application scopes according to the idea of the embodiments of the present application. In conclusion, the content of this specification should not be construed as a limitation to the present application. 

What is claimed is:
 1. An encryption method comprising: generating a keystream for encrypting a part of data in a first message that is an initial layer-3 or tracking area update (TAU) request message, wherein a length of the keystream is equal to a length of the part of the data and is less than a length of the first message, wherein the part of data comprises small data; generating, by performing an exclusive OR operation on the keystream and the first message, a second initial layer-3 or TAU request message in which only the part of the data is encrypted, wherein the second message comprises an encryption indication indicating that the part of the data is encrypted; and sending the second message to a network equipment.
 2. The method according to claim 1, wherein the generating the first keystream comprises: setting a value of a length parameter to be equal to the length of the part of the data; and generating the keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm.
 3. An encryption method comprising: generating a keystream by (i) setting a value of a length parameter to be equal to a length of a first message that is an initial layer-3 or tracking area update (TAU) request message; (ii) generating the keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm; (iii) acquiring, according to a format of the first message and a length of a part of data in the first message, a start bit and a stop bit of the part of the data; and (iv) reserving bits that correspond to bits from the start bit to the stop bit in the generated keystream, and replacing other bits except the bits from the start bit to the stop bit in the keystream with 0; performing an exclusive OR operation on the keystream and the first message to generate a second message that is an initial layer-3 or TAU message in which only the part of the data is encrypted; and sending the second message to a network equipment, wherein the second message comprises an encryption indication, and the encryption indication indicates the part of the data in the second message is encrypted.
 4. The method according to claim 1, wherein generating the keystream comprises: setting a value of a length parameter to be equal to a length of a variable or a length of the first message; generating the keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm; and truncating the first keystream according to a length of the part of the data, wherein a length of the truncated first keystream is the same as a value of the length of the part of the data.
 5. The method according to claim 1, wherein the encryption indication comprises at least one of the following: (a) an integrity-protected and partly ciphered parameter in a security header type parameter; and (b) a small-data transmission indication.
 6. A decryption method comprising: receiving a first message that is an initial layer-3 or a tracking area update (TAU) message, wherein the first initial layer-3 message comprises data and only a part of the data is encrypted, wherein the encrypted part of the data includes small data and the first message includes an encryption indication indicating the part of the data in the first message is encrypted; generating a keystream according to the encryption indication, wherein the keystream is used to decrypt only the part of the data in the first message and a length of the keystream is equal to a length of the part of the data and is less than a length of the first message; and generating, by performing an exclusive OR operation on the keystream and the first message, a second message that is also an initial layer-3 or TAU message in which the part of the data is decrypted.
 7. The method according to claim 6, wherein the generating the keystream comprises: setting a value of a length parameter to be equal to a length of the small data; and generating the keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm.
 8. A decryption method comprising: receiving a first message that is an initial layer-3 or a tracking area update (TAU) message, wherein the first message comprises data and only a part of the data is encrypted, wherein the encrypted part of the data includes small data and the first message includes an encryption indication indicating the part of the data in the first message is encrypted; generating a keystream according to the encryption indication, wherein the keystream is used to decrypt only the part of the data in the first message, wherein generating the keystream includes, (i) setting a value of a length parameter to be equal to a length of the first message; (ii) generating the keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm; (iii) acquiring, according to a format of the first message and a length of a part of data, a start bit and a stop bit of the part of the data; and (iv) reserving bits that correspond to bits from the start bit to the stop bit in the generated keystream, and replacing other bits except the bits from the start bit to the stop bit in the keystream with 0; and generating, by performing an exclusive OR operation on the keystream and the first message, a second message that is also an initial layer-3 or TAU message in which the part of the data is decrypted.
 9. The method according to claim 6, wherein the generating the keystream comprises: setting a value of a length parameter to be equal to at least one of a length of (a) a variable in the first message and (b) the first message; generating the keystream by using the evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm; and truncating the keystream according to a length of the part of the data, wherein a length of the truncated keystream is the same as the length of the part of the data.
 10. The method according to claim 9, wherein the generating, by performing the exclusive OR operation on the keystream and the first message, the second message in which the part of the data is decrypted comprises: generating, by performing the exclusive OR operation on the keystream and the part of the data, the second message in which the part of the data is decrypted.
 11. The method according to claim 6, wherein the encryption indication comprises at least one of the following: (a) an integrity-protected and partly ciphered parameter in a security header type parameter; and (b) a small-data transmission indication.
 12. An encryption apparatus comprising a processor and a transmitter, wherein the processor is configured to: (a) generate a keystream for encrypting a part of the data in a first message that is an initial layer-3 or tracking area update (TAU) request message, wherein a length of the keystream is equal to a length of the part of the data and is less than a length of the first message and the part of the data comprises small data; and (b) generate, by performing an exclusive OR operation on the keystream and the first message, a second initial layer-3 or TAU request message comprising an encryption indication indicating the part of the data is encrypted; and the transmitter is configured to send the second initial layer-3 or TAU request message to a network equipment.
 13. The encryption apparatus according to claim 12, wherein in generating the keystream, the processor is configured to: set a value of a length parameter to be equal to a length of the part of the data; generate the keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm.
 14. An encryption apparatus comprising a processor and a transmitter, wherein the processor is configured to (a) generate a keystream for encrypting part of data comprising small data in a first message that is an initial layer-3 or a tracking area update (TAU) message, wherein generating the keystream includes, (i) setting a value of a length parameter to be equal to a length of the initial layer-3 message; (ii) generating the first keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm; (iii) acquiring, according to a format of the initial layer-3 message and a length of the part of the data, a start bit and a stop bit of the part of the data; (iv) reserving bits that correspond to bits from the start bit to the stop bit in the generated keystream; and (v) replacing other bits except the bits from the start bit to the stop bit in the first keystream with 0; (b) generate, by performing an exclusive OR operation on the keystream and the first message, a second initial layer-3 or TAU request message comprising an encryption indication indicating the part of the data is encrypted; and wherein the transmitter is configured to send the second initial layer-3 or TAU request message to a network equipment.
 15. The encryption apparatus according to claim 12, wherein in generating the keystream, the processor is configured to: set a value of a length parameter to be equal to at least one of (a) a length of a variable in the first message, and (b) a value of a length of the first message; generate the keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm; and truncate the keystream according to a length of the part of the data, wherein a length of the truncated keystream is the same as a value of the length of the part of the data.
 16. A decryption apparatus comprising a receiver and a processor, wherein the receiver is configured to receive a first message that is an initial layer-3 or tracking area update (TAU) message comprising data and only a part of the data is encrypted, wherein the encrypted part of the data includes small data and the first message includes an encryption indication indicating the part of the data in the first message is encrypted; and wherein the processor is configured to (a) generate a keystream according to the encryption indication in the first message, wherein the keystream is used to decrypt only the small data contained in the first message and a length of the keystream is equal to a length of the part of the data and is less than a length of the first message, and (b) generate, by performing an exclusive OR operation on the keystream and the first message, a second message that is also an initial layer-3 or TAU message in which the small data is decrypted.
 17. The decryption apparatus according to claim 16, wherein in generating the keystream, the processor is configured to: set a value of a length parameter to be equal to a length of the part of the data; and generate the keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm.
 18. A decryption apparatus comprising: a receiver configured to receive a first message that is an initial layer-3 or tracking area update (TAU) message, wherein the first message comprises data and only a part of the data is encrypted, the encrypted part of the data includes small data, and the first message includes an encryption indication indicating the part of the data in the first message is encrypted; and a processor configured to (a) generate a keystream according to the encryption indication in the first message, wherein the keystream is used to decrypt only the small data contained in the first message and generating the keystream includes, (i) setting a value of a length parameter to be equal to a length of the initial layer-3 message; (ii) generating the keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm; (iii) acquiring, according to a format of the initial layer-3 message and a length of the encrypted part of the data, a start bit and a stop bit of the part of the data; and (iv) reserving bits that correspond to bits from the start bit to the stop bit in the generated keystream and replace other bits except the bits from the start bit to the stop bit in the keystream with 0; and (b) generate, by performing an exclusive OR operation on the keystream and the first message, a second message that is also an initial layer-3 or TAU message in which the small data is decrypted.
 19. The decryption apparatus according to claim 16, wherein in generating the keystream, the processor is configured to: set a value of a length parameter to be equal to at least one of the following: (a) a length of a variable in the first message, and (b) a length of the first message; generate the keystream by using an evolved packet system encryption algorithm, wherein the length parameter is used as an input parameter of the algorithm; and truncate the keystream according to a length of the part of the data, wherein a length of the truncated keystream is the same as the length of the part of the data.
 20. The decryption apparatus according to claim 19, wherein in generating the decrypted second message, the processor is configured to perform the exclusive OR operation on the keystream and only the encrypted part of the message. 